Method of heat casting refractory blocks



H. T. SMYTH METHOD OF HEAT CASTING REFRACTORY BLOCKS Filed Mayfaz, 1940Aug. 24, 1943.

. attendant decrease in volume.

`Patented Aug. 24, 1943 METHOD OF HEAT CA BLO STING REFRACTORY CKSHarold T. Smyth, Louisville, Ky.,

assignor to Corhart Refractories Company, Louisville, Ky., a corporationof Delaware Application May 22, 1940, Serial No. 336,645

4 Claims.

Useful refractories can 'be made by electrically melting refractorycompositions and casting to shape in suitable molds. During thesubsequent cooling, liquid resolidies to a nonporous highly crystallinerefractory, the crystallization proceeding gradually proportion to thelatent heat dissipated from the surface. Since, however, the volume ofanir crystalline refractory material is less than the volume occupiedwhen melted, a pipe will be produced if the mold is jus't filled., This4internal flow' in a casting is obviously objectionable for anyrefractory which is required Ito resist failure by corrosion, as, forexample, glass refractories. Onel method of decreasing the pipe is tosupply additional molten material from a font reservoir above Vthe gate'from which additional material can drain into the casting after partialsolidiiication has occurred. This technique is limited by the fact thatthe font casting is'also freezing at inward from each mold surface in esubstantially the same rate as the main casting, I

so that in order for molten material to be available at the last stagesof crystallization of the main casting, the font must be substantiallyas large as the casting itself. -This is obviously uneconomlcal, andinpractice a font with perhaps 10% of the volume of the casting isnormally employed which although relatively efficient still leaves apipe.

l This economical procedure was further improved by the Fulcher Patent1,700,288 and during the past few years thousands of tons of4 heat castrefractories have been made in that way. Inv

that procedure a sand mold surrounded by insulating powder is lled withmolten material through a font mold of insufficient volume to preventpipe formation. In both the font mold and the sand mold solidificationtakes place from the Y outside, draining of perhaps 30 to 50% of themolten material in the font occurring, however, due to the solidicationin the sandmold with When'the font shell is exhausted of its molten corehowever,

further decrease in Volume produces a pipe within the casting. Whensolidication of the 'cast-l ing is almost complete, the font mold andinsulating powder are removed from the top of the casting and the fontshell broken away exposing the pipe. A new font mold is placed aroundthe opening and the pipe filled with additionalv molten material. While,as stated, this procedure has been followed in the production of a largequantity of refractories it has been attended with considerable loss dueto cracked castings.

Htherto an the period of and top sand Fig. 4, illustrating the useerroneous belief as to the determining factors in this cracking hasprevented the reduction of loss, but'I have discovered the correcttheory and have invented a procedure by which it may be reduced if notentirely prevented and such invention forms thesubject-matter of thisapplication. Briefly stated it involves the early removal of the fontshell after the initial pouring, and the proper thermal protection ofthe upper face of the cast block immediately adjacent to the pipe duringsolidication of such initial pour. It also includes smoothing such faceof the block immediately after removing .the font shell. x

Fig. l lis a cross sectionlthrough the sand mold and iron font mold.

Fig. 2 is a view'similar to Figure 1, showing the font mold removed andthe top of the sand mold and font shell covered with insulating powder.

Fig. 3 is a cross section, showing the font shell slab removed. g

Fig. 4 is a cross section showing the application of the heat-insulatingcover andthe covering of the casting with the insulating powder.

Fig. 5 is a view similar to Figure 4, illustrating the castingapproaching solidiflcation and the formation of septa. v

Fig. 6Y is a cross section somewhat 4similar to of a plaque'to preventthe insulating powder from entering the pipe in the casting.

Referring to the accompanying drawing which represents successiveoperations in carrying out my improved procedure, Figure 1 illustrates acondition existing at such time after the initial pour that a rigid wallm has formed inside the 1 sand mold l and the iron font mold 2 due tothe loss of heat from these surfaces and the molten material has juststarted to drain downward from the font shell '1L through the gate 4 inthe top slab la of the sand mold l. At this stage the iron font mold 2is removed, and the font shell and top of the sand m'old covered withinsulating powder 5 (see Figure. freezing of molten materalin the fontshell so that a larger proportion drains into the casting.

In Figure 2, the refractory in the sand mold hasv partly solidified andthe molten material has drained completely from the font leaving in thelatter the successive septa 6 extending across the pipe in the fontshell. The pipe 6 in the block gate. At this time (which is definite fora definite size) the font shell is pulled offand the top sandA slab lremoved (see Figure 3) I have discovered that if the font shell isremoved at this stage the 2) which delays the i irregular refractoryprotuberances left by such removal around the rim of the gate can beeasily removed by a scraper, together with any sand adhering to the topof the casting, while after a longer period of -waiting the refractoryprotuberances are strong and the sand immediately beneath the font shelltends to fuse tightly to the casting. The upper end of the pipe is thencovered by a refractory and heat insulating cover I I, and the top ofthe casting re-covered with the insulating powder (see Figure 4). Whensolidiiication of the casting is almost complete,I

a pipe 6 will be formed crossed irregularly with septa 6b (see Figure 5)At this stage the insulating powder is brushed off the top of thecasting around the pipe and the cover I l removed, the font moldput backinto place over the pipe, the septa broken through with a bar and thepipe refilled with molten refractory. This refilling process can berepeated if found necessary. The casting is finally annealed.

Particularly with thin blocks breakage is apt to occur if excessiveforce is required to break through the font septa En. I have discovered,however, that these septa are easilybroken down if this is done shortlyafter formation It istherefore advantageous'to break these down one byone as they are formed which can be done by removing momentarily therefractory gate cover Il at intervals and poking with a bar. In this waythe pipe can be kept open to its maximum width andthe pieces which fallinto the liquid 9 are frozen into the bottom portion of the casting oneby one rather than all at once in a small area, where they may producestrains or inhomogeneities in crystal growth.

The refractory coverl for the gate is conveniently made ofa good gradeof lire brick which may be backed, if greater insulation is desired,with a less refractory insulating brick, or a compositerefractory-insulating brickmay be used.

casting operation, I have found it convenient to make the cover in twosections. The first section consists of a plaque, Ila Figure 6, as thickas the desired layer of insulating powder 5, with a hole in the centeras large as the gate 4 in the top slab. 'I'his section of the cover isleft v 1n position throughout the casting operations 1. The method ofmaking solid cast refractories which includes pouring molten materialintc a mold provided with a gate through a font mold of volumeinsuilicient to prevent pipe formation, removing the font mold, breakingaway the font shell formed therein atthe completion of the draining ofmolten materialtherefrom, protecting the space which was below the gatewith a heat conserving cover during a substantial part of thesolidication which produces the pipe, thereafter removing the cover andlling the pipe with additional molten material.

2. The method of making solid cast refractories which includes pouringmolten material into a mold provided with a gate through a font mold ofvolume insufcient to prevent pipe formation, removing the font mold,breaking away the font shell formed therein at the completion of thedraining of molten material therefrom, smoothing the top of the castingaround the space which was below the gate, protecting such space with aheat conserving cover during a substantial part of the solidiiicationwhich produces the pipe, thereafter removing the cover and filling thepipe with additional molten material.v

3. The method of making solid cast refractory ies which includes pouringmolten material into a moldv provided with a gate through a font mold ofvolume insuiiicientto prevent pipe forpart of the solidiiication whichproduces the pipe, removing said cover from time to time and punchingdown the septa as formed in the pipe during such solidiiication,thereafter removing the cover and iillingthe pipe with additional moltenmaterial. J

4. The method of making solid cast refractories which includes pouringmolten material into a mold provided with a gate through a font mold asubstantial part of the solidiiication which produces the pipesfremovingthe cover, refilling the pipe with additional molten material through athe added material, thereafter removing the cover and refilling withmolten material the pipe produced during such solidliication.

f HAROLD T. SMYTH.

